Multiple element electric fuse



V. A. GRZECZKOWSKI 3,145,282

MULTIPLE ELEMENT ELECTRIC FUSE I Aug. 18, 1964 Filed May 14, 1962 F/GJ.

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United States Patent 3,145,282 MULTIPLE ELEMENT ELECTRIC FUSE Vincent A. Grzeczltowsld, Newtown Square, Pa, assignor g? (general Electric Company, a corporation of New Filed May 14, 1%2, Ser. No. 194,326 5 Claims. (Cl. 290-131) This invention relates to an electric fuse of the type that comprises a plurality of fusible elements connected in parallel and imbedded within a pulverulent arcquenching material such as quartz sand. More specifically, the invention related to a fuse of this type in which the fusible elements are helically wound about cores of insulating material that extend longitudinally of the fuse in laterally spaced-apart relationship.

When a sand-filled fuse is subjected to a short circuit current, the usual fusible element immediately vaporizes, and an arc is established through the metallic vapors along the path formerly occupied by the fusible element. The surrounding sand serves to cool the metallic vapors and thereby provide an arc-quenching action that ordinarily results in the desired circuit interruption. The sand, however, does not remain intact during this interrupting operation. The intense heat of the arc melts the sand immediately surrounding the arc and converts this portion of the sand from a high resistance material into a semi-conducting one until substantial cooling occurs. The melted portion of the sand about a fuse element is referred to hereinafter as a fulgurite. Where one or more fuse elements are helically wound about a core, it is important that the portion of the fulgurite along one turn of the fuse element not merge longitudinally of the core with the portion of the fulgurite along an adjacent turn since such a merger tends to shorten the effective arcing path and reduce the length of sand available for arcquenching, thus impairing the interrupting ability of the fuse. To minimize the chances for such a merger, it is important that the turns of the helically wound element or elements be spaced apart along the core by at least a predetermined amount.

Increased spacing of the turns of a helically wound element can be provided by increasing the effective periphery of the core about which the element is wound so as to thus reduce the number of turns consumed by a given length of element, but this approach can be carried only so far because it is also important that the parallel-connected fuse elements of adjacent cores not be too close together. Otherwise, the fulgurites about these parallel elements will merge, and this too can lead to impaired interrupting ability. These problems can, of course, be overcome by increasing the volume of the fuse to make available more space between the cores and parallel-connected fuse elements, but this approach is frequently uneconomical and results in a fuse of excessive size.

Accordingly, an object of the present invention is to so locate and shape the cores of the fuse that during the interrupting operation exceptionally efiicient use is made of the volume of sand available within the fuse housing.

Another object is to so locate and shape the cores that the desired spacing between the turns of each helicallywound fuse element can be obtained without substantially increasing the chances for merger of the fulgurites of the fuse elements on adjacent cores and without increasing the volume of the fuse as compared to prior fuses of this character and corresponding rating.

In carrying out the invention in one form, I provide an electric fuse comprising a tubular housing of insulating material having a centerline extending longitudinally thereof. Within the housing are mounted a plurality of elongated insulating cores extending longitudinally of the 3,145,282 Fatented Aug. 18, 1964 housing in angularly-spaced relationship about the centerline. Each of the cores comprises a body portion extending longitudinally of the housing and a plurality of ribs each extending along the length of the body portion and radiating outwardly therefrom. Fusible elements are wound helically about the cores with the fusible elements on each core being supported at the free ends of said ribs. The ribs of each of said cores project from the body portion of the core by an amount that locates adjacent sections of the fusible elements on adjacent cores in reference planes that extend longitudinally of the fuse in substantially parallel relationship. A pulverulent arcquenching material is disposed within the housing and surrounds the fusible elements and cores along their length.

For a better understanding of this invention, reference may be had to the following description taken in conjunction with. the accompanying drawings, wherein:

FIG. 1 is a side elevational view partly in section showing a fuse embodying one form of the present invention.

FIG. 2 is a cross sectional view taken along the line 22 of FIG. 1.

FIG. 3 is a cross sectional view similar to that of FIG. 2 of a modified fuse.

Referring now to FIG. 1, there is shown a multiple element fuse comprising an elongated cylindrical housing ll? of insulating material provided at its opposite ends with electrically conductive terminals 12 and 14. Mounted within the housing 10 are a plurality of cores 16 of a ceramic material extending longitudinally of the housing in laterally spaced-apart relationship. As can be seen in FIG. 2, these cores 16 are symmetrically located about the longitudinal central axis 9 of the housing it). The cores are held in their symmetrical position shown by means of spacer plates 17 fixed to the housing 14 at each end of the fuse. The cores are suitably secured to each of the spacer plates 17 by suitable attaching means, such as a tab 13 bent out of a connector 23, soon to be described.

Helically wound about each of the cores are several fusible elements 2.6 of a wire form. Each of these fusible elements 2i) extends from one end of the core to the other and is wound about the core in uniformly spacedapart relationship relative to its adjacent fusible element on the same core. The fusible elements 20 on a given core are electrically connected together at each end of the core so that they are in parallel circuit relationship. This end connection is shown at 22, 23. Each of the parts 23 is a conductive connector projecting through an opening in the end plate 17 for connecting the fusible elements on a given core to the terminal 12. The connector 23 is preferably welded or soldered to the terminal 12. The fusible elements on a given core are electrically connected to this connector 23 either by being directly welded to the connector 23 or by means of a conductive wire 22 which is wound about the core 16, the connector 23, and the ends of the fusible elements 20. This wire 22 also holds the connector 23 and the other fusible elements to the core 16. It is to be understood that other similar end connections may alternatively be used.

It will be noted from FIG. 2 that each core 16 comprises a plurality of ribs 30 radiating outward from a central body portion 32 where the ribs are joined together. The outer end of each rib 30 is referred to hereinafter as the free end of the rib. The cores are of a substantial uniform cross-sectional shape throughout their length, so that the ribs may be thought of as extending longitudinally of the body portion along the entire length of the core. When a fusible element 26 is wound about a core, it is supported at the free ends of the ribs 30, and the portion of the element that extends between the free ends of adjacent ribs follows a straight line path and is 3 spaced from the body portion of the core by a recess 34, as illustrated in FIG. 2.

The space inside the housing about the cores 16 is filled with a pulverulent arc-extinguishing material such as quartz sand, indicated at 25 in FIG. 1. This sand extends all the Way out to the interior surface of the housing 10 and along the entire length of the fuse, so that the fusible elements 20 are imbedded in the sand along substantially their entire length. The presence of recesses 34 between the ribs of the core enables sand to be present even between the core and the fusible elements.

Although we prefer to wind several elements 20 about each core 16, it is to be understood that the invention is also applicable to fuses where only a single element is wound about each core.

A fuse performs its protective function by interrupting the electric circuit therethrough in response to excessive currents. In this respect, when a current of high magnitude flows through a fusible element 2t), it rapidly heats the fusible element, causing it to immediately vaporize. This establishes an arc through the metallic vapors along the path formerly occupied by the fusible element. When a plurality of wires are wound about a single core, a plurality of parallel arcs are established along the respective paths formerly occupied by the fusible elements. This, of course, occurs for the fusible elements on each core. The surrounding sand serves to cool the metallic Vapors and thereby provide an arc-quenching action that ordinarily results in the desired circuit interruption. The sand, however, does not remain intact during this interrupting operation. The intense heat of each arc melts the sand immediately surrounding the arc and converts this portion of the sand from a high resistance material into a semiconducting one until the melted sand, or fulgurite, cools.

It is important that the fulgurites formed about the fuse elements on a given core not merge longitudinally of the core. In other words, the portion of the fulgurite about one turn of wire should not merge longitudinally of the core with the portion of the fulgurite about an adjacent turn of wire. Such a merger tends to shorten the effective length of the arcing path, bypassing turns of the fusible elements, and reducing the amount of sand available for effective arc-quenching action, thus impairing the interrupting ability of the fuse.

In the disclosed fuse, such mergers of the fulgurites along the length of the core are virtually eliminated by maintaining a predetermined minimum spacing between the adjacent turns of the fusible elements on a given core. The effective periphery of each core, as viewed in a transverse cross-section such as depicted in FIG. 2, is of great enough length to permit fusible elements of the required length to be wound about the core with the required minimum spacing between the turns and no unwound length remaining.

Not only is it important to prevent the fulgurites from merging along the length of each core but it is also important to prevent the fulgurite about fusible elements on one core from merging with the fulgurite about the fusible elements on an adjacent core. Such mergers can lead to impaired interrupting ability by upsetting the current distribution between the fusible elements and cansing one or more of the arcing paths to carry an excessive portion of the total current. To prevent such fulgurite mergers, I maintain a predetermined minimum spacing between the fusible elements on adjacent cores. This minimum spacing is large enough to prevent the fulgurites from merging even during interruption of maximum rated current.

One of the objects of this invention is to locate and shape the cores so that this minimum spacing between the fusible elements on adjacent cores can be obtained without substantially increasing the volume of the fuse as compared to prior fuses of this character and rating. This object is achieved in the fuse of FIGS. 1 and 2 by provid- A ing each core with three ribs Stl projecting from the body portion 32 by an amount that locates adjacent straight line sections of the fusible elements on adjacent cores in planes which are substantially uniformly spaced from each other or parallel to each other. For exarnple, in FIG. 2 the sections 4% of fusible element 20 are located in a reference plane 42 that is substantially parallel to a reference plane 44- that contains the adjacent straight line sections 46 of a fusible element wound on an adjacent core.

By establishing the optimum spacing required to prevent fulgurite merger and then providing only this spacing and no more between adjacent sections, such as 40 and 46, of the adjacent fusible elements, I am able to make the most efi lcient use of the sand that is present in the fuse. No substantial amount of excess sand is present between the adjacent sections such as 4-0 and 46, and thus the volume of housing 1% can be held to a virtual minimum.

Another way of describing the shape and location of the cores of FIG. 2 is with reference to imaginary reference planes 5t) that include the central axis of the housing lit) and radiate outwardly therefrom in angularly spaced relationship. The reference planes 50 extend between each pair of adjacent cores and divide the interior of the fuse into volumes of ector-shaped cross section. The adjacent sections, such as 40 and lb, of the fusible elements on adjacent cores are disposed in reference planes 42 and 44 located generally parallel to the reference plane 50 located between the two cores.

It will also be noted that the body portions 32 of the core N are located in angularly-spaced reference planes 52 that include the central axis of the housing 10. Projecting from the body portion of each core toward the central axis f is a rib that is located in this reference plane 52. The other two ribs are generally symmetrical with respect to this reference plane 52. This configuration contributes to the generally uniform spacing between the adjacent sections 4b and 46 of the fusible elements on adjacent cores.

The spacing between the interior surface of the housing 10 and the fusible element 20 is also of some importance. It is most desirable that this spacing be large enough to prevent the fulgurites formed upon fuse operation from contacting the housing since this could result in excess heating of the housing and the possible formation of an arcing path along the interior surface of the housing. The disadvantage of making this spacing large, however, is that such enlargement unduly increases the diameter of the fuse housing. I, therefore, make the spacing only large enough to prevent the fulgurite from contacting the housing during the most severe rated interrupting conditrons.

The heat dissipation characteristics of the fuse under continuous current conditions depend to an important extent upon the minimum spacing between the fusible elements of the fuse. The greater this minimum spacing, the better will be the heat dissipation characteristics and the lower will be the hottest spot temperature in the fuse. For a given fuse volume, the disclosed fuse provides a larger minimum spacing between the fusible elements than is present in comparable prior designs. This larger minimum spacing is made possible by the generally uniform spacing that is present between adjacent sections, such as 40 and 46, of adjacent fusible elements, thus permitting more efficient use of the sand that is present.

In the modified fuse design of FIG. 3, there are fewer cores 16 than in FIG. 2, and each core has four instead of three ribs 30 projecting from its central body portion 32. The two designs do, however, have a number of features in common. One of these is that adjacent sections 40 and 46 of the fusible elements on adjacent cores are located in planes 42 and 44 that are substantially uniformly spaced, or parallel. Also, the interior of the fuse housings shown in FIG. 3 can be divided into volumes of secamazes tor-shaped cross section by reference planes 5% corresponding to the reference planes 50 of FIG. 2, and the adjacent sections it) and 46 of the fusible elements on adjacent cores are located in planes did and 42 parallel to these reference planes 50. Also, one rib of each core projects from its body portion 32 toward the central axis and is located in a reference plane 52 that includes the body portion and the central axis 9. The presence of these relationships in FIG. 3 contributes to highly efiicient use of the sand available Within the housing in in essentially the same manner as pointed out relative to FIG. 2.

Although the space at the center of the disclosed fuse is illustrated as being filled only with sand, it is to be understood that it can, if desired, be used for an indicator element, such as a coiled element imbedded in the sand of the fuse.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects, and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

' 1. An electric fuse comprising:

(a) a tubular housing of insulating material having a central extending longitudinally thereof,

(b) said housing having a space therein consisting of a plurality of volumes of sector-shaped cross section bounded by reference planes including said central axis and radiating outwardly therefrom in angular-lyspaced relationship,

(0) a plurality of elongated insulating cores mounted within said housing and extending longitudinally of said housing in angularly-spaced relationship about said central axis,

(d) said cores being respectively located in said sectorshaped volumes,

(2) each of said cores comprising a body portion and a plurality of ribs each extending along the length of said body portion and radiating outwardly from said body portion,

(6') fusible elements wound helically about said cores with the fusible elements on each core being sup ported at the free end of said ribs,

(f) the ribs of each of said cores being so disposed that the fusible element Wound about the core is spaced from an adjacent reference plane by a substantially uniform distance over those sections of the fusible element that extend between those ribs of the core located adjacent said reference plane,

(g) a pulverulent arc-extinguishing material contained within said housing and surrounding said fusible elements and cores.

2. An electric fuse comprising:

(a) a tubular housing of insulating material having a a central axis extending longitudinally thereof,

(b) a plurality of elongated insulating cores mounted within said housing and extending longitudinally of said housing in angularly-spaced relationship about said central axis,

(c) each of said cores comprising a body portion extending longitudinally of said housing and a plurality of ribs each extending along the length of said body portion and radiating outwardly from said body portion,

(0?) fusible elements wound helically about said cores with the fusible elements on each core being supported at the free end of said ribs,

(e) the ribs of each of said cores projecting from the body portion of said core by an amount that 10- cates adjacent sections of the fusible elements on adjacent cores in reference planes that extend longitudinally of the fuse in substantially parallel relationship,

( f) said reference planes radiating outwardly from the central region of said fuse.

3. The fuse of claim 2 in which body portions of said cores are disposed in angularly-spaced planes that extend longitudinally of the fuse housing and include the longitudinal central axis of the fuse, one rib of each of said cores extending from said body portion toward said central axis and being located in the plane that includes said body portion, additional ribs projecting from the body portion of said core transverse to said plane that includes said body portion and generally symmetrical with respect to said plane that includes said body portion.

4. The fuse of claim 2 in which each of said cores comprises three ribs radiating from the body portion of the core, the body portions of said cores being disposed in angularly-spaced planes that extend longitudinally of the fuse housing and include the longitudinal central axis of the fuse, one rib of each of said cores extending from said body portion toward said central axis and being located in the plane that includes said body portion, the other two ribs of said core projecting from the body portion of the core transverse to said plane that includes said body portion at acute angles to said plane that includes said body portion and generally symmetrically-located with respect to said plane that includes said body portion.

5. The fuse of claim 2 in which each of said cores comprises four ribs radiating from the body portion of the core, the body portions of said cores being disposed in angularly-spaced planes that extend longitudinally of the fuse housing and include the longitudinal central axis of the fuse, one rib of each of said cores extending from said body portion toward said central axis and being located in the plane that includes said body portion, two of the remaining ribs projecting from the body portion of said core substantially normal to said plane that includes said body portion, the remaining rib projecting from said body portion away from said central axis.

References Cited in the file of this patent UNITED STATES PATENTS 2,672,540 Dewey Mar. 16, 1954 2,972,031 Cox Feb. 14, 1961 FOREIGN PATENTS 153,412 Sweden Sept. 14, 1953 214,610 Australia Nov. 15, 1956 

2. AN ELECTRIC FUSE COMPRISING: (A) A TUBULAR HOSING OF INSULATING MATERIAL HAVING A A CENTRAL AXIS EXTENDING LONGITUDINALLY THEREOF, (B) A PLURALITY OF ELONGATED INSULATING CORES MOUNTED WITHIN SAID HOUSING AND EXTENDING LONGITUDINALLY OF SAID HOUSING IN ANGULARLY-SPACED RELATIONSHIP ABOUT SAID CENTRAL AXIS, (C) EACH OF CORES COMPRISING A BODY PORTION EXTENDING LONGITUDINALLY OF SAID HOUSING AND A PLURALITY OF RIBS EACH EXTENDING ALONG THE LENGTH OF SAID BODY PORTION AND RADIATING OUTWARDLY FORM SAID BODY PORTION. (D) FUSIBLE ELEMENTS WOUND HELICALLY ABOUT SAID CORES WITH THE FUSIBLE ELEMENTS ON EACH CORE BEING SUPPORTED AT THE FREE END OF SAID RIBS, (E) THE RIBS OF EACH OF SAID CORES PROJECTING FROM THE BODY PORTION OF SAID CORE BY AN AMOUNT THAT LOCATES ADJACENT SECTIONS OF THE FUSIBLE ELEMENTS ON ADJACENT CORES IN REFERENCE PLANES THAT EXTEND LONGITUDINALLY OF THE FUSE IN SUBSTANTIALLY PARALLEL RELATIONSHIP, (F) SAID REFERENCE PLANES RADIATING OUTWARDLY FROM THE CENTRAL REGION OF SAID FUSE. 